Landing gear lock



Sept. 18, i1945.

R. F. DREIFKE LANDING GEAR LOCK Filed July 26, 1945 2 shee'ts-sheet 1 INVENTOR RAYMOND E DREIFKE BY ATTORN EY Q sept. 1s, 1945.

R. FQDREIFKE LANDING GEAR LOCK Filed July 26 1943 2 Sheets-Sheet 2 INVENTOR RAYMOND E DREIFKE ATTORNEY Patented Sept. 18, 1945 UNITED STATES PATENTv OFFICE LANDING GEAR LOCK -Raymond F.

Delaware Dreifke, St. Louis, Mo., assignor to Curtiss-Wright Corporation,

a corporation of Application July 26, 1943, Serial No. 496,235

2 Claims.

to lock the foldable strut in the down position,

are costly, require conduits and swivel connections, are diillcult to maintain and the parts thereof are often inaccessible.

It is an object of the present invention to pro` vide a locking device for landing gear which is simple in construction, cheap to build, easy to install, and readily accessible for inspection and repair.

It is another object of the invention tc provide a locking device wherein the usual conduits and :iwivel connections are not needed for its operaon. f

It is still another object of the invention to provide a locking device which, in addition to serving as a lock, actually assists in forcing the lgear mn its locked down position.

According to the present invention, a pair of toggle links are connected to the foldable `strut adjacent the pivot connection of the two arms of the same and to the shock strut. Groups of springs serve to throw the toggle links into over center position and` in so doing, forcibly straighten the arms of the foldable strut to put thereby the landing gear into its final down position. Thus, the lock springs th'emselves assist in the lowering of the landing gear. A power retracting unit is connected to the landing gear struts through one of the toggle links of the locking device at a point rearwardly of," the pivotal connection of the toggle link to the shock strut so that force is taken directly from the unit to return the toggle links from theirlocked over center position to permit the retraction of 1anding gear. Means is provided in the connection of thetoggle springs to the toggle links wherebyif any of the springs are broken, the pulling force p of the other springs is not disturbed. l"

For'other objects and for a better understanding of the invention, reference may be had to the following detailed description taken in connection with the 'accompanying'.` drawings, in` which f Fig. l is a fragmentary perspective view of landing gear in its retracted position and its connection to an airplane wing structure, the landing gear in its down position being indicated in broken lines.

the'/ able pivot support member I Fig. 2 is an enlarged plan view ofthe locking device. i

Fig. 3 is an elevational view of the locking device.

\ Fig. 4 is also an elevational view of the device but showing the parts thereof in a collapsed position and with the brace strut folded into its retracted position.

Fig. 5 is an enlarged sectional view of the connection of the locking'device to the shock strut as taken on line I-l of Fig. 2. i x

Fig. 6 is an enlarged sectional view of the means for connecting the toggle springs to the toggle links.

Referring now tothe figures, the landing gear is comprised of a main hydraulic shock strut il, 4 il., carriedin a suitwhich pivots about an axis I2 on a rear spar I2 of an aircraft wing structure I4. A whee1 il mounted on the ground end of the shock` strut il is of a usual construction, and is adapted tofit. when the landing gearis retracted, within engine cowling il on the wing structure i4.

To one side of shock strut il and some distance from the wheel end thereof, is shown the pivotal connection I1 for a two-part foldable drag or brace strut I8. The drag strut il is pivotally connected to a pivot support member I2 on a forward wing spar 2li of the wing structure il. A brace strut 2|, positioned laterally and anslarly of the shock strut il, is pivoted at i1 and also in the pivotal axis il for the shock strut Il adjacent a laterally/ spaced support member 22 in alignment for connection to rear spar Il. The drag or brace strut I8 consists of a lower link arm 2l and an upper link arm 24 pivotally connected at a knee joint 25 intermediate the span of the arms when straightened. For the purpose of lat. eral rigidity of upper arm 24, a brace 2l is provided. This brace 26 is welded to arm 24 at 21 and the opposite end is pivoted to a support member 2l. It should now be apparent that when the knee joint 25 is bent inwardly, the main shock strut i2 can be rotated forwardly and upwardly to accomplish the retraction of the entire gear. At the same time drag strut arms 2l and 24 fold inwardly and finally assume a folded position as shown in Figs. l and 4. The knee pivot 2B scribes llinks 30 and 3| and a set of six coil springs 32 in groups ofthree which are positioned respectively upon each side of thelinks, Fig. 2. The link 35 is of U- or channel-shaped cross section and is pivoted at 32 toa bracket 33 welded on the shock strut I intermediate theslength thereof. Link 3l is pivoted at 34 to the upper drag strut arm 24 and an adjustable threaded coupling 35 is provided on this link to permit length adjustments. A pivot connection-33 between links 33 and 3l is effected through the provision of a nose portion 31 welded on link 3| and adapted to tit or nest within the U-shaped link 30, Figs. 3 and 4. The foregoing linkjsystem acts as a toggle and in which a set of toggle springs acts above the pivot 3l to force the links 30 and 3i into locking position. In order to permit the toggle springs 32 to operate overceht'er, a short post 33 and brace member 33 are welded to the link 3| as shown. A pair of spring anchor plates 4| and 42 are then pivotally mounted at the upper end-of the short post 33, Fig. 8. These plates 4| and 41 are welded to a split trunnion tube, the two halves of which are indicated atA 43 and 44. Alignment of these trunnion halves is achieved by providing a V-slot 45 in part 43 and a mating V-projection 43 in' part 44. This trunnion is carried in a tubular journal 41 which is inserted and welded in a suitable aperture 4l in-the end of brace 38. A thru-bolt 49 and nut 50 secure this trunnion and spring anchor plate unit in assembly.

The cooperation between the two groups of springs 3,2. Which has :been achieved through the inter-locked trunnion elements 43 and 44, is an important feature of the locking system. The full eiIect of each spring 32 is obtained only when its extended length is substantially maintained Thus, considering only the spring group acting on trunnion part 43 and with this trunnion part free of locking engagement with part 44, when all three springs are fully operating, the system is symmetrical and balanced. But if one of the outside lsprings should break, then the remaining two springs-would rotate the plate and thus shorten the springs to an extent suillcient to decrease the holding force thereof. Hence, any realignment of these springs such that their set length is decreased lessens the locking force on the links 33 and 3l. With each set of springs locked together by means oi' the trunnion lock 43-44, damage to any one or more springs on either side does not disturb the full force of the remaining springs to any harmfulextent. It should also be noted that the combined spring load, tending to maintain links 30 and 3l in axial alignment, has been chosen so that rough landings or manual efforts to raise the link pivot 38 will be prevented. Furthermore, substantially all of the forces acting on links 30 and 3| are either tension or compression. Hence, the bending forces at pivot 33 are theoretically zero. Consequently, thefspring force could be reduced to almost the zero point for adequate locking. But due to unforeseen shocks and unusual forces, the spring force is rather large or approximately 150 pounds. An identical arrangement of spring anchor plates and trunnion elements is also provided on the link 33 at 5I. Thus, the toggle springs are positioned to permit the link pivot 33 to pass upwardly therebetween.

The toggle link 30 is adapted to be rotated about pivot 32 by means of piston rod 52 of a main -retracting piston-cylinder unit 53, which expands upon retraction of the landing gear and collapses upon extension of the landing gear. The unit 53 is carried on bracing structure 54 such that the entire unit may pivot with respect thereto. The piston rod 52, in turn, is aillxed to the link 30 at a pivot 55, Fig. 5. Considering the action of the retracting cylinder unit 53, it is evident that the rst action in retraction is to rotate link 30 about pivot 32 in a clockwise direction (Fig. 3) through a sufiicient arc to carry the link pivot 33' above the line of force of the springs v32.- lDuring the time the toggle isbeing broken, the knee .loint 25 is also being broken.

Once the toggle links 30 and 3l and drag strut I3 have been broken, the cylinder unit 53 acts to retract the whole gear, and the same is moved to the full line position shown in Figs. 1 and 4.

The force system of the retracting unit 53, the link system 30 and 3|, and the springs 32 will now be examined so that the function of the several elements will be clear. In the landing position of the gear. the links 30 and 3i form a straight arm such that the pivots 34, 33, and 32 are all in the same line. 'I'he force direction of springs 32 may be taken asyacting in a line'drawn between pivots 49 and El, and since this torce line is above the line 34--3 5-32. the spring force acts through post arm 33 to produce a negative or locking rotational moment about pivot l38. Uponretraction unit 53 exerts a positive force at 55; and since this force is behindV the Divot 32 of link 30, `a positive or unlocking rotational movement is produced in link 30. The opposition to the retracting unit force by the toggle spring force will exist until the pivotal point 33 between links .30 and 3| has been moved upwardly to a location abovethe spring force line between pivots 49 and 5i. At this latter` position of pivot 38, the spring forces assist the retracting unit 53 in the collapse of the locking link and ldrag strut system. In the retracted position, the landing gear is retained by a hydraulic latch mechanism 53 engageable with a pin 51 on the shock strut I0.

It should now be apparent that there has' been provided a locking device for the foldable strut of landing gear which is cheap to construct, easy to instalLand readily accessible for inspection and repair.

iWhile various changes may be made in the detending between the fcldable brace strut and the shock strut for locking the foldable brace strut in its extended and straightened position, said toggle link arrangement including toggle links pivotally connected together and connected respectively t0. the brace and shock struts, stop means preventing relative movement of the toggle links beyond the slightly over center position, tension springs connected between the toggle linksv tending to urge the links to a locking position against the stop means when in over center position and tending to urge the links to a collapsed position when short of center position, and said retracting unit for the landing gear connected to one of the toggle links at a point removed from its pivotal connection with one o! the struts whereby the power for retracting the landing gear is applied through the toggle link to at rst return the toggle links from their over center locking position to thereby unlock the toggle link arrangement. l

2. In an airplane, a supporting structure, a retractable landing gear connected to the supporting structure, said landing gear including a shock strut and a foldable brace strut for bracing the shock strut in its down position, said foldable brace strut having two link arms pivotally connected together, a power unit for retracting the landing gear, and a toggle link arrangement extending between the foldable brace strut and the shock strut for locking the foldable brace strut in its extended and straightened position, said toggle link arrangement including toggle links pivotally connected together and connected respectively to the brace and shock struts, stop means preventing relative movement of the toggle links beyond a slightly over center position, a pair of groups of .tension springs spaced one above the other and connected between the toggle links tending to urge the links to a locking position against the stop means when in over center position and tending to urge the links to a collapsed position when short of center position, one group being located at one side of the toggle links while the other group is located at the opposite side of the toggle links, and means for so pivotally connecting the groups of springs to the toggle links that the groups are tied together and relative movement of one group with respect to the other group is prohibited, whereby upon breakage or release of any one of the springs, the pulling force of the remaining springs is left unaiected.

" RAYMOND F. DREIFKE. 

